Electron transfer followed by double fragmentation reactions: mechanism ofphotogeneration of tertiary amines and radicals from tetraorganyl borates

The double fragmentation reactions of N,N,N-tributyl-N-acetobenzo[b]thiophe ne ammonium berates have been investigated, The primary step in the cleavag e reactions is electron transfer from the berate anion to the excited accep tor. This generates radical pairs that decompose by rapid carbon-nitrogen a nd carbon-boron bond fragmentation. Transient spectra and photoproducts are consistent with this bond cleavage, Tertiary amines are formed as a result of reductive carbon-nitrogen bond scission. The boranyl radicals formed un dergo oxidative carbon-boron bond cleavage to generate alkyl or phenyl radi cals, depending on the structure of the borate. Both cleavage processes are irreversible, and their rates easily exceed the rate of the back electron transfer reaction. The net quantum yields for photodecomposition are also h igh. Detailed mechanistic studies were carried out. (C) 1999 Elsevier Scien ce S.A. All rights reserved.